1. Field of the Invention
The present invention relates to a partly bent electric circuit substrate in which the parts are partly bent so as to be exposed to the surface while being disposed in a narrow space as in the circuit substrate to be contained in the cell box of a notebook type personal computer. More particularly, the invention relates to a partly bent electric circuit substrate which can be partly bent without requiring a space while using a low priced print substrate or the like and which can be reliably electrically connected between the substrates on both sides of the bent part, and a method for its manufacture.
2. Description of the Prior Art
The cell box of a notebook type personal computer is constituted so that, as shown for example in FIG. 3(b), a rechargeable secondary cell such as a lithium ion cell is contained in the cell containing part 22 in a resin case 21, so that an electric circuit substrate 23 having a protective circuit for preventing the secondary cell from being over-charged or short-circuited to be exploded and destroyed is contained in the narrow space between the cell containing part 22 of the resin case 21 and the end part of the case 21. Moreover, on the electric circuit substrate 23 there are provided a switch 25, an LED 26 for displaying the cell charge condition, etc., and further a terminal pin for the connector 27 for connection with the power source for charging or for supply of power to the drive circuit for a notebook type personal computer being soldered thrusting through the through-hole of the electric circuit substrate. And, the switch 25 and the LED 26 are required to appear on the surface, and the connector 27 must be inserted in an appropriate position of the connector containing part 29 of the case 21.
As it is necessary for the circuit substrate to be formed so as to be contained in a narrow space and to have the LED part and others appear on the surface with accurate position setting with the notched part of the set, it has been the conventional practice to assemble the circuit parts 28 using an electric circuit substrate 23 comprising a flexible substrate made by providing a flexible film of polyimide or the like with wiring (not illustrated) of copper foil or the like. And, assembly work is manually made by inserting the circuit forming part in the narrow space as mentioned above, bending the part to be exposed outside, so that the connector 27 is contained in the connector containing part 29. It may be conceivable to have the connector 27 secured to the connector containing part 29 of the case 21 in advance and insert the through-hole of the electric circuit substrate 23 in the connector pin. However, in the flexible substrate, the bent part is curved and its shape cannot be established, and therefore the position setting of the through-hole of the electric circuit substrate cannot be accurately made, and soldering is difficult due to the springy nature of the curved condition. For these reasons, it has been practiced to assemble, as described above, with the connector 27 previously soldered to the electric circuit substrate 23.
On the other hand, there is disclosed in Japanese Patent Publication Unexamined No. HEI 8-330727 a method for obtaining a substrate which can be bent at a free angle so made that, in connecting the electric circuit substrates, as shown in FIG. 4, two electric circuit substrates 31 and 32 are disposed on the same split substrate 30, the two substrates are connected by a plated wire 33, after which the split substrate 30 is split by a split groove 34 to make the two electric circuit substrates 31, 32 electrically connected and the substrate bent at a free angle.
The electric circuit substrate which requires to be inserted in a narrow gap and to be partly bent can be formed into small size by being furnished in high density through the use of a flexible substrate as described above, and simply bent, so that the desired parts such as LED can be disposed at approximately a certain place. However, the flexible substrate is very expensive in comparison with the organic epoxy type substrate and costly. Furthermore, as the bent portion does not show plastic deformation and not show constant bending angle, the position setting cannot be accurately carried out, and stress is exerted to the soldered part or the mounted electric parts at the time of the insertion of the connector to show lowering of reliability, or the bent portion is required to be adhered by both side adhesive tape or the like. Moreover, it is weak in mechanical strength as a substrate for the switch, and a reinforcing material is required on the reverse side thereof. In addition, the wiring of the flexible substrate comprises copper foil of very thin thickness of 35 .mu.m, through which no large current can be led. Therefore, there is a problem in complication of manufacturing process leading to higher cost and lower reliability.
The method of connecting the two circuit substrates by the plated wire is accompanied with the necessity to provide the substrates on both sides with through-holes for insertion of the plated wire, and also to insert the plated wire into the through-holes and secure it by soldering. If the aim is only to make electrical connection of the two substrates, such a method is desirable in securing connection, but for the requirements for inserting in a narrow space, bending a part so as to have the predetermined parts only expose in front, and yet to make electric connection with sufficient electric capacity through the bent part, said method involves a problem that it is not possible to insert in the narrow space due to the projections formed on both the surface and the reverse side of the substrate. In other words, because the conventional method is to insert a plated wire in the substrate in a manner to form an arc and solder it on the reverse side of the substrate, on the substrate surface there is required a thickness corresponding to the thickness of the arc portion, and on the reverse side of the substrate there is necessitated to project a plated wire and solder the projection. Furthermore, there is a problem in connecting with the plated wire that, notwithstanding the difficulty of bending and especially sharp angle bending, the cross-sectional area is small and large current is less easily run. Such a point did not occur as problematic matter in the technique disclosed in Japanese Patent Publication Unexamined No. HEI 8-330727 as it was free from the requirements of providing the substrate in a narrow space and exposing only a part of the content on the surface.